Specifications

The NMEA 0183 Information sheet - Issue 3

The different versions of the

NMEA 0183 standard

As the NMEA 0183 specication has slowly evolved over

the years, connecting one device to another is not always

a simple matter.

The situation is further complicated, as many manufacturers

still use the old (“single ended”) method of connection

because it is cheaper to implement.

So how can an older type NMEA device be connected

to a newer type device? Care is needed – it is possible

to damage or overload the output of a newer differential

device if it is incorrectly connected to an older device. This

is because the older devices used ground as the return,

whereas the newer devices actually drive the NMEA “-/

B” line between 5v and 0v. Thus, connecting this output

to ground will result in high currents being drawn by the

driver instrument, resulting in potential overheating and

damage to the driver circuits.

See pages 8 and 9 for connection diagrams relating to

interconnection of different NMEA 0183 bus and device

congurations.

Format changes

The data format is largely the same between versions

of NMEA, with v2.0 adding some extra sentence strings,

and removing older (redundant) sentence strings from the

specication.

There are however problems when interfacing between

version 1 and 2 NMEA 0183 where some sentence

formatters were changed between the two standards. This

means that some older equipment will not work properly

when receiving data from equipment sending version 2.0

data. These changes are too fundamental and detailed to

go into in this document.

Introducing ISO-Drive

To solve all the above fundamental interfacing problems,

Actisense introduced ISO-Drive outputs on all new

products. These outputs provide the essential isolation

that will keep a system safe when mixing products from

different manufacturers on a complex marine bus. If the

ISO-Drive “B” line is connected to ground, no current will

ow and the system is safe.